Question

Define the octet rule and write its significance and limitations.

Answer 1

Part 1: Octet rule:

• The octet rule states that atoms combine either by transfer of valence electrons from one atom to another (gaining or losing) or by sharing of valence electrons to have an octet i.e., eight electrons in their valence shells.

Part 2: Significance of octet rule:

• The octet rule helps to explain the chemical bonding in a chemical compound.
• The octet rule illustrates the types of chemical bonding like covalent, ionic, and coordinate bonds.

Part 3: Limitations of octet rule:

• Incomplete octet: In certain molecules such as BeH_2, and BeCl_2, BF_3, the central atom has less than 8 electrons in its outermost shell, yet these molecules are stable.
• Expanded octet: In certain molecules such as PF_5, and SF₆ the central atom has more than 8 electrons in its outermost shell, yet these molecules are stable.
• For Hydrogen (H) to attain stability, it needs to share, gain or lose 1 electron. It does not need to complete an octet to attain stability.
• Helium (He) has only 2 electrons and is stable.